The present invention relates to hydroaminomethylation of olefins. Aliphatic amines are useful in a variety of applications including agrochemical and pharmaceutical products and intermediates, as well as precursors for polymers such as polyurethanes. The homogeneous hydroaminomethylation reaction was reported by Reppe at BASF (Liebigs Ann. Chem. 1953, 582, 133–161) using a homogeneous cobalt carbonyl catalyst. This reaction consists of a tandem, one-pot olefin hydroformylation/reductive amination sequence in which the intermediate aldehyde reacts with a primary or secondary amine to form an imine or enamine intermediate, which undergoes hydrogenation to form a secondary or tertiary amine. U.S. Pat. No. 3,513,200 reports the use of a homogeneous rhodium triphenylphosphine catalyst for synthesis of tertiary amines via hydroaminomethylation. The use of hydroaminomethylation with ethylene to form n-propylamines was reported by Jones in J. Organomet. Chem. 1989, 366, 403–408. This reaction was completely selective for normal propylamines since ethylene hydroformylation can produce only a single regioisomer of the intermediate priopionaldehyde. Eilbracht et al. reported in Tetrahedron 1999, 55, 9801–9816 that pharmacologically active amines can be prepared by hydroaminomethylation using a homogeneous [Rh(cod)C1]2 catalyst, however this reaction proceeded with low selectivity to the desired branched regioisomer. Beller et al reported in J. Am. Chem. Soc. 2003, 125, 10311–10318 that terminal alkenes can undergo hydroaminomethylation with very high selectivity to the linear amine isomer by use of a rhodium catalyst which employs the Xantphos diphosphine ligand. In Science 2002, 297, 1676–1678, Seayad et al. describe the preparation of aliphatic amines by reacting an internal olefin (e.g., 2-butene, 2-pentene, or 2-octene) with an amine (e.g., piperidine, dimethyl amine, or di-n-hexylamine) in the presence of syngas, a phosphine ligand, and a cationic procatalyst, [Rh+(cycloocta-1,5-diene)2] [BF4−] (also known as [Rh(cod)2BF4]procatalyst). The researchers also tested a monodentate phosphite ligand under the same reaction conditions but discovered poor amine selectivity—and no conversion to the desired linear amine—from which they concluded that “phosphite ligands are less suitable for the desired reaction because of hydrolysis problems encountered in the presence of water and amines.” Id. at 1677. This reported shortcoming of phosphite ligands in hydroaminomethylation is significant since rhodium phosphite catalysts are very useful for olefin hydroformylation, the first step of the hydroaminomethylation sequence. Pruett (J. Org. Chem. 1969, 34, 327) reported that the homogeneous rhodium triphenylphosphite catalyst gave higher linear selectivity than the rhodium triphenylphosphine. Bulky monodentate phosphite ligands, such as tris(2-tert-butyl-4-methylphenyl)phosphite, were found by van Leeuwen et al (Organometallics 1995, 14, 34–43) to give very high hydroformylation rates under mild conditions. Bidentate bisphosphite ligands can give very high selectivity to linear aldehydes from rhodium-catalyzed hydroformylation of terminal olefins. These catalysts are highly tolerant of a wide range of functional groups which makes their application to the synthesis of complex organic molecules possible (J. Am. Chem. Soc. 1993, 115, 2066–2068). Intramolecular examples of hydroaminomethylation of unsaturated amines were reported by Bergmann et al. (Tetrahedron. Lett. 1997, 38, 4315–4318) using a highly regioselective bisphosphite ligand.
To ensure hydrogenation of the enamine intermediate to the desired amine, Seayad et al. report that “it is desirable to attain a reaction temperature of 120° C.” Id. at 1677. On the other hand, in a later publication (Angew. Chem. Int. Ed. 2003, 42, 5615–5619) the same research group report the selective preparation of the enamine intermediate using a [Rh(CO)2(acac)] procatalyst and a phosphine ligand at temperatures in the range of 65° C. to 125° C.
Although alkyl amines can be made with reasonably high yield and selectivity using the method described by Seayad et al., the requirement of high temperatures makes the method suitable only for olefins, amines, catalysts, and products that are stable at these advanced temperatures. Also, long reaction times require extended use of process equipment, which result in increased processing costs. Accordingly, it would be desirable to find a more efficient and effective way of aminomethylating olefins.